The present invention relates generally to a welding-type system and, more particularly, to a system and method for controlling an open-circuit voltage supplied by the welding-type power source under various conditions.
There are many welding-type systems that are used for a variety of applications. Some welding-type systems, as used herein, include welding systems, plasma cutting systems, and induction heating systems. Accordingly, welding-type power, as used herein, refers to welding, plasma cutting, or induction heating power. One primary component of these welding-type systems is a welding-type power supply that delivers welding-type power conditioned to perform a specific welding-type process. Often, a particular power supply will have a topology and a control scheme chosen or optimized for a particular welding-type application or to deliver a particular welding-type power. For example, a welding power supply might be designed for a metal-inert gas (MIG), tungsten-inert gas (TIG), or stick welding process, to name but a few.
Some welding-type applications utilize a wire feeder that drives a consumable wire electrode to perform a desired welding-type process, such as a MIG welding process. One common type of wire feeder is a voltage sensing wire feeder. Voltage sensing wire feeders, as used herein, include wire feeders that derive operational power from the output voltage provided by a welding-type power supply to drive a desired welding process. Generally, voltage sensing wire feeders become active when the voltage and/or current provided by an associated power supply increases above a threshold value. In this regard, the wire feeder does not typically receive control signals or communicate with the power supply. Because the wire feeder derives operational power from the output of the welding-type power supply, the welding-type power supply must continuously provide a minimum amount of power needed to operate the wire feeder, even during open circuit conditions.
Generally, a typical voltage sense wire feeder requires approximately 1 to 10 watts of power to operate in an idle state and, often, requires in excess of 150-200 watts in a jog or weld state when the wire feeder motor is running. The actual power required is dependent on motor design, wire feed speed and torque. To this end, in an effort to accommodate various design concerns, welding-type power supplies typically provide an output voltage of approximately 15 to 44 volts when driving a welding process, but provide an increased voltage (e.g., approximately 70-80 volts) under open circuit conditions. The increased open circuit voltage helps to create and stabilize the arc. While this increased open circuit voltage (OCV) is desirable for weld process performance, the relatively high OCV is undesirable in some circumstances. For example, a higher voltage will possibly cause the user discomfort in the event the user touches both outputs.
To this end, some attempts have been made to design a power supply or device capable of providing a reduced OCV. However, prior attempts are generally not well-suited for inverter-based, DC welding-type power supplies, especially with the capability to power a voltage sensing wire feeder with reduced open circuit voltage during the idle and jog states.
For example, some phase controlled welding-type power supplies have been designed to provide a reduced OCV. However, these phase controlled welding-type power supplies are, generally, not capable of providing a broad range of power outputs needed to power a wide variety of welding-type processes. That is, unlike inverter-based or “switched” power supplies, phase controlled welding-type power supplies are typically limited to powering stick or MIG welding-processes. Beyond being able to act as a “multi-process” welding-type power source, inverter-based power supplies are often desirable due to a decreased size and weight over other welding-type power supplies, such as phase controlled welding-type power supplies.
Accordingly, voltage reducing devices have been developed that can be arranged between an inverter-based power supply and a welding load and/or wire feeder. These autonomous devices are designed to reduce the open-circuit voltage available at the welding torch. However, such autonomous voltage reducing devices (VRD) have a number of drawbacks. First, these VRDs add to the complexity of the overall system by requiring an autonomous device to be coupled with the welding-type system. Second, since these VRDs are connected between the output terminals of the welding-type power supply and the welding torch, only the OCV available at the welding torch is reduced and the OCV at output terminals of the welding-type power supply is not reduced. Third, these VRDs are not designed to accommodate some devices and processes, such as voltage sensing wire feeders and trigger jogs, because they are generally unable to adequately distinguish between the power draw by a voltage sensing wire feeder or a trigger jog that occurs during open-circuit conditions and initiation of a welding-type process
Therefore, it would be desirable to have a switched or inverter-based, DC welding-type power supply capable of powering a voltage sensing wire feeder during idle, jog, and welding conditions, but without delivering an undesirable OCV. Furthermore, it would be desirable to have such a welding-type power source capable of driving a wide variety of welding-type processes with and without voltage sensing wire feeders. Additionally, the reduced open circuit voltage should not interfere with arc starting and arc stability.